When you need an anonymous name for a real or hypothetical woman, call her Jane Doe. Unnamed women in court cases are often referred to as Jane Doe.
Jane Doe is someone whose name can't legally be used, or who simply doesn't want it used. In the case of a man, you'd call him John Doe. The need for a placeholder name comes up from time to time in legal cases — and sometimes people use the term Jane Doe to mean "an average, ordinary woman," or an unidentified patient or crime victim. John Doe has been used since the mid-1700's, with Jane Doe following soon after.